Electronically controlled space-division concentration systems generally use electromechanical relay matrices or reed relay matrices. The disadvantages of such systems are mainly related to price and bulk; in a telephone concentrator the relay matrices account for about half the price and the volume of the equipment and it does not seem possible to hope for a substantial improvement to this situation, with this type of equipment.
This is why a great amount of work has been done aiming at using integrated circuits to embody space concentration. Two families of components can mainly be used for this application, namely, PNPN thyristors and field effect transistors of the metal-oxyde-semiconductor (MOS) type or complementary (C-MOS) transistors. Existing thyristor cross points are capable of withstanding voltages in the order of 50 to 100 volts and currents of a few tens of milliamperes, this being insufficient for transmitting the supply current of the line nor the ringing current with the necessary safety margin. It is therefore indispensable to separate the signalling and transmission functions, as is the case also with cross points formed by MOS transistors, but further, the control circuits for the thyristor cross points are more complex because the direct holding current of the connection systems must be injected and extracted and the interfaces of connection with conventional TTL or MOS integrated circuits are not easy to produce.
C-MOS complementary transistors have electric characteristics enabling them to fulfill transmission, crosstalk and distortion requirements. This is why thyristors are at present substituted in some embodiments by MOS and C-MOS transistors with which it is possible to produce space-division matrices whose cross points are MOS or C-MOS transistors; such matrices formed by integrated circuits are also currently found in trade.
Quite obviously, the cross points are fixed and such matrices do not provide full versatility of use necessary for producing concentrators; the addressing of these matrices in particular must take into account all the cross points of the matrix.
The invention concerns a space concentrator using C-MOS integrated circuits but not having the drawbacks of known space matrices.
The object of the present invention is to provide a switching network which can readily be embodied with presently available integrated circuits and in particular, preferred embodiments of the present invention provide versatile concentrator modules having several applications. Indeed, if a telephone exchange is arranged to accept plug-in modules according to preferred embodiments of the present invention then the same modules can be used interchangeably as first or second stage switches in a two-stage network and can also be used interchangeably with callers of differing calling rates; all the necessary arrangements particular to the switching stage or to the calling rate being made in the exchange wiring external to the concentrator module.
The present invention provides a switching network comprising a matrix of cross-point switches disposed in a pattern at selected ones of the cross-points in an array of mutually orthogonal inlets and outlets, wherein the pattern of selected cross-points is built up from a rectangular array of basic layouts each comprising eight cross-point switches distributed among the sixteen cross-points formed by a group of four consecutive inlets crossing a row of four consecutive outlets; the basic layouts being of two types; a first type having its switches at the outer cross-points of its odd numbered lines and at the inner cross-points of its even numbered lines and a second type having its switches at its other cross-points; basic layouts of both types being disposed in a pattern over the array in such a manner that all the cross-point switches are arranged in a single matrix not equivalent to a plurality of separate matrices with interleaved inlets and outlets.
The pattern of basic layout types is preferably a binary pattern such that the matrix has a first line of alternating types of layout, a second line of alternating pairs of layout types and so on each n-th line having its layouts in sets of 2.sup.n-1 layouts of each type.
Preferably the last line is composed entirely of layouts of one type. The lines of the matrix are preferably constituted by rows of outlets and the lines of the basic layouts by their outlets.
In a preferred application the switching network is a concentrator having a greater number of inlets than outlets, say 32 to 16 giving a concentration factor of 2.
A plurality of switching networks may be connected with their outlets commoned together to provide a greater degree of concentration.
At least some pairs of adjacent inlets or alternatively pairs of adjacent outlets may be connected together to provide at least some inlets having full access to all the outlets or outlets having full access to all the inlets as the case may be.
The outlets are preferably constituted by analogue multiplexers e.g. integrated circuit packages having analogue switches in the form of MOS transistors.
Two stages of switching network may be provided and with suitable design devices it can be arranged that a single plug-in design of modular switch matrix can be used in all parts of the two stage network including parts which are intended for heavy traffic since the requisite pairing of inlets or outlets can be performed externally to the switch matrix.